When a new treatment becomes available, physicians must decide whether or when to adopt it into their practice. Knowledge of the results of randomized clinical trials and consensus conference recommendations do not necessarily ensure the adoption of appropriate treatments. Breast-conserving surgery became recognized as an appropriate option for many women with early breast cancer in the 1980's. We have already studied, in a cross-sectional fashion, the use of breast-conserving surgery by Medicare patients in 1986, and have demonstrated large differences in its use during that year, with utilization ranging from 3.5% to 21.2% in different states. Women treated in the South Atlantic, South Central and West North Central regions are less likely to receive the treatment. We, and others, have also shown the association of several patient and hospital characteristics with the use of breast-conserving therapy in that year. Specifically, patients under age 55 or over age 79 were more likely to receive conservative treatment Black women and patients with axillary nodal metastases were less likely. Patients treated at larger hospitals, urban hospitals, teaching hospitals, and hospitals with radiation or geriatric services were more likely to receive conservative therapy. While these factors were significant in predicting use of conservative surgery, they explained relatively little of the geographic variation we documented. The overall purpose of this proposal is to attempt to better understand the assimilation of new treatments into practice, by studying the temporal adoption of breast-conserving surgery over time, and to examine the effects of various possible determinants of the temporal adoption of the treatment. Our specific aims are as follows: 1. Elucidate the effect of hospital characteristics, physician characteristics, and local area characteristics (ethnic, economic, educational, and seasonal) as predictors of the temporal adoption of breast-conserving surgery from 1984 to 1992. 2. Determine the effect of state legislative requirements for patient information regarding breast cancer treatment options on the assimilation of breast conserving surgery. 3. Determine the effect of early exposure to the technique of breast- conserving surgery (within the framework of clinical trials) on the subsequent early or late adoption of the treatment. This study will identify the dynamics of the diffusion of breast- conserving surgery by developing stochastic models using the longitudinal treatment data from 1984 to 1992.